Picosecond Electron Transfer and Stimulated Emission in Reaction Centers of Rhodobacter sphaeroides and Chlorofelxus aurantiacus

Becker, Michael E.; Middendorf, D.; Woodbury, Neal W.; Parson, W. W.; Blankenship, R.E.

doi:10.1007/978-3-642-82918-5_101

Cited by 11 publications

(8 citation statements)

References 8 publications

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“…From the transient absorption and picosecond photodichroism data obtained with these RCs it was concluded that the nature of the primary intermediate I~ was the same as in RCs of purple bacteria (Kirmaier et al 1983(Kirmaier et al a, 1984. However the primary charge separation to P + I~ took 8-13 ps (Kirmaier et al 1986;Becker et al 1986), i.e. about 3-4 times longer than in purple bacterial RCs.…”

Section: Charge Separation In Bacterial Photosynthetic Reaction Centresmentioning

confidence: 86%

“…12. Schematic view of the chromophores in the purple bacterial reaction centres as determined by (Deisenhofer et al 1984) P = bacteriochlorophyll dimer (special pair); BChl L M = bacteriochlorophyll monomers in L and M subunits; BPh, M = bacteriopheophytins in L and M subunits; Q A = primary quinone acceptor; Fe = non-haem iron (taken from Becker et al 1986).…”

Section: Charge Separation In Bacterial Photosynthetic Reaction Centresmentioning

confidence: 99%

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Applications of ultrafast laser spectroscopy for the study of biological systems

Holzwarth

1989

Quart. Rev. Biophys.

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The discovery of mode-locked laser operation now nearly two decades ago has started a development which enables researchers to probe the dynamics of ultrafast physical and chemical processes at the molecular level on shorter and shorter time scales. Naturally the first applications were in the fields of photophysics and photochemistry where it was then possible for the first time to probe electronic and vibrational relaxation processes on a sub-nanosecond timescale. The development went from lasers producing pulses of many picoseconds to the shortest pulses which are at present just a few femtoseconds long. Soon after their discovery ultrashort pulses were applied also to biological systems which has revealed a wealth of information contributing to our understanding of a broadrange of biological processes on the molecular level.It is the aim of this review to discuss the recent advances and point out some future trends in the study of ultrafast processes in biological systems using laser techniques. The emphasis will be mainly on new results obtained during the last 5 or 6 years. The term ultrafast means that I shall restrict myself to sub-nanosecond processes with a few exceptions.

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Section: Charge Separation In Bacterial Photosynthetic Reaction Centresmentioning

confidence: 86%

Section: Charge Separation In Bacterial Photosynthetic Reaction Centresmentioning

confidence: 99%

Applications of ultrafast laser spectroscopy for the study of biological systems

Holzwarth

1989

Quart. Rev. Biophys.

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“…viridis structure suggest that electrostatic interactions with the tyrosine lower the energy of the state P+B-, thus aiding electron transfer along the L side (10). In the RCs of the thermophilic bacterial species Chloroflexus aurantiacus, this tyrosine residue is replaced by leucine, which may explain the slower electron-transfer kinetics observed there (11). Moreover, the aromatic ring of the tyrosine could act as a conduit for an electron, as has been suggested for electrontransfer processes in some heme proteins.…”

mentioning

confidence: 92%

Effect of specific mutations of tyrosine-(M)210 on the primary photosynthetic electron-transfer process in Rhodobacter sphaeroides.

Nagarajan

Parson

Gaul

et al. 1990

Proc. Natl. Acad. Sci. U.S.A.

133

132

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We have measured the rate of the initial electron-transfer process as a function of temperature in reaction centers in a native strain of the photosynthetic bacterium Rhodobacter sphaeroides and two mutants generated by sitedirected mutagenesis. In the mutants, a tyrosine residue in the vicinity of the primary electron donor and acceptor molecules was replaced by either phenylalanine or isoleucine. The electron-transfer reaction is slower in the mutants and has a qualitatively different dependence on temperature. In native reaction centers the rate increases as the temperature is reduced, in the phenylalanine mutant it is virtually independent of temperature, and in the isoleucine mutant it decreases with decreasing temperature. At 77 K, the electron-transfer reaction is "30 times slower in the isoleucine mutant than in the native. These observations support the view that tyrosine-(M)210 plays an important role in the electron-transfer mechanism. In the isoleucine mutant at low temperatures, the stimulated emission from the excited reaction center undergoes a time-dependent shift to shorter wavelengths.In purple photosynthetic bacteria, light initiates a series of electron-transfer reactions in a pigment-protein complex known as the reaction center (RC). X-ray crystallographic studies have shown that the pigments of the RC are arranged symmetrically on two protein subunits, L and M (1-3). Light absorption excites a bacteriochlorophyll dimer designated as P. Near P are two "accessory" bacteriochlorophylls (BL and BM), two bacteriopheophytins (HL and HM), and two quinones. The excited dimer (P*) transfers an electron to HL in "'3 ps (4-6). Why excitation reduces only one of the two bacteriopheophytins is not yet clear (7,8). Moreover, no consensus exists on the function of the accessory bacteriochlorophylls. Although BL is located between P and HL, several ultrafast spectroscopic studies (4,5,9) (Fig. 1) (1-3). The corresponding residue on the opposite side is phenylalanine. Calculations based on the Rp. viridis structure suggest that electrostatic interactions with the tyrosine lower the energy of the state P+B-, thus aiding electron transfer along the L side (10). In the RCs of the thermophilic bacterial species Chloroflexus aurantiacus, this tyrosine residue is replaced by leucine, which may explain the slower electron-transfer kinetics observed there (11). Moreover, the aromatic ring of the tyrosine could act as a conduit for an electron, as has been suggested for electrontransfer processes in some heme proteins. These considerations lead naturally to employing site-directed mutagenesis to explore the factors that determine direction and rate of the initial electron-transfer reaction. Using picosecond absorption spectroscopy, we have measured the electron-transfer kinetics in RCs EXPERIMENTAL PROCEDURES Oligonucleotide site-directed mutations were constructed by the phosphorothioate selection method (13). A 1.3-kilobase (kb) Sal I-Hind III DNA restriction fragment carrying the M gene of the bacterial ...

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“…It was stated (14,15) that the electron is directly transferred from the excited special pair (P*) to H and from there to the quinone QA. There was no generally accepted experimental evidence of an intermediate electron-carrying state B- (16)(17)(18)(19)(20)(21)(22)(23). The postulated direct electron transfer from P to H imposed numerous difficulties on the theoretical description of the charge-transfer process (24)(25)(26)(27)(28)(29)(30)(31)(32)(33)(34)(35)(36)(37)(38) …”

mentioning

confidence: 99%

Initial electron-transfer in the reaction center from Rhodobacter sphaeroides.

Holzapfel

Finkele²,

Kaiser³

et al. 1990

Proc. Natl. Acad. Sci. U.S.A.

293

170

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The initial electron transfer steps in the photosynthetic reaction center of the purple bacterium Rhodobacter sphaeroides have been investigated by femtosecond timeresolved spectroscopy. The experimental data taken at various wavelengths demonstrate the existence of at least four intermediate states within the first nanosecond. The difference spectra of the intermediates and transient photodichroism data are fully consistent with a sequential four-step model of the primary electron transfer: Light absorption by the special pair P leads to the state P*. From the excited primary donor P*, the electron is transferred within 3.5 ± 0.4 ps to the accessory bacteriochlorophyll B. State P+B-decays with a time constant of 0.9 ± 0.3 ps passing the electron to the bacteriopheophytin H. Finally, the electron is transferred from H-to the quinone QA within 220 ± 40 ps. According to present knowledge, an electron is transferred upon light absorption from the P along branch A to the quinone QA (8)(9)(10)(11)(12)(13) Materials and Experimental TechniquesRCs from two strains ofRb. sphaeroides, the wild-type strain (ATCC 17023) and the carotenoid-free strain (R 26.1), were isolated as described (39). The measurements were performed at room temperature (297 K) in cuvettes with a 1-mm path length with stirring. The concentration of the samples was adjusted to OD8w values between 0.5 and 1.0 mm' A synchronously pumped unidirectional ring dye laser (42) generated pulses with a duration of 60 fs at a wavelength of 860 nm. The energy of single pulses was increased to 20 lJ by a three-stage dye amplifier (repetition rate, 10 Hz). Each of these pulses was split into two parts. (i) The excitation pulse was focused to a 0.5-mm spot providing an energy density of not more than 100 uJ/cm2 in the sample. In the probed volume, -7% of the RCs were excited per pulse. This low excitation density prevents double excitation of the RC and related nonlinear processes. The exciting pulse, centered at 860 nm, had a bandwidth of <15 nm (full width at half-maximum). No spectral components of the exciting pulse were detected at wavelengths of <840 nm. Thus only the lowest electronic level ofP at 860 nm was excited. (ii) The probing pulse passed an adjustable delay line and was focused onto a 1-mm-thick jet of ethylene glycol to generate a femtosecond white-light pulse. A 10-to 20-nm-wide portion of this continuum was selected by means of a special dispersion compensating monochromator (43). The energy of the probing pulses was <7 p.J/cm2.

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Picosecond Electron Transfer and Stimulated Emission in Reaction Centers of Rhodobacter sphaeroides and Chlorofelxus aurantiacus

Cited by 11 publications

References 8 publications

Applications of ultrafast laser spectroscopy for the study of biological systems

Applications of ultrafast laser spectroscopy for the study of biological systems

Effect of specific mutations of tyrosine-(M)210 on the primary photosynthetic electron-transfer process in Rhodobacter sphaeroides.

Initial electron-transfer in the reaction center from Rhodobacter sphaeroides.

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